A mixture of a polycarbonate and a styrenic resin such as ABS resin, SAN resin and so forth has high heat resistance and impact resistance, so that it is generally used, as a polymer alloy, for various shaped or molded articles such as parts for an automobile, electric products, electronic products and the like. When the polymer alloy is employed for a housing, an enclosure, a chassis or the like of electric or electronic parts or office automation (OA) apparatus or instruments, flame-retardancy or fire-resistance is required of such a polymer alloy.
In particular, for increasing the safety of a product, a standard qualification of V-O or 5V is recently frequently required of a shaped article of an OA apparatus or a home electric product. While the V-O or 5V standard is the highest flame-retardancy level according to the Subject 94 of Underwriter's Laboratory Co., Ltd. (hereinafter briefly referred to as UL) it is used as the flame-retardancy standard in U.S.A.
On the other hand, in order to decrease the amount of material used, miniaturization and also making the part or the housing thinner is useful. Such part or housing has, however, a risk of a fire drip arising from the thinned part of the shaped article accompanied with burning (combustion), and thus spreading fire to another inflammable or combustible substance. Accordingly, a flame-retardant resin composition is also required for such a higher flame resistance or flame-retardancy so as not to cause a flame drip.
For imparting the flame-retardancy, a halogen-containing flame-retardant is usually added to a polymer alloy comprising a polycarbonate and a styrenic resin. As the halogen-containing flame-retardant, there may frequently be employed a combination of a bromine-containing flame-retardant exemplified as tetrabromobisphenol A or its oligomer, a brominated epoxy oligomer, and a flame-retarding-auxiliary comprising, as a main component, a metallic oxide exemplified as antimony trioxide. It is, however, pointed out by an organization for environmental protection in Europe that, among such bromine-containing flame-retardants, use of decabromodiphenyl ether (DBDPE) or octabromodiphenyl ether (OBDPE) possibly generates toxic dibenzodioxin with burning of the resin composition. Therefore, a non-halogen-containing flame-retardant is useful for making a flame-retardant (flame-proofing) resin.
As the non-halogen-containing flame-retardant, a phosphorus-containing flame-retardant, specifically a flame-retardant comprising an aromatic phosphoric acid ester is employed. For example, U.S. Pat. No. 5,061,745 corresponding to Japanese Patent Application Laid-open No. 32154/1990 (JP-A-2-32154) discloses the use of a flame-retardant comprising a monomeric phosphoric acid ester in combination with polytetrafluoroethylene as a flame-retarding-auxiliary. U.S. Pat. No. 5,204,394 discloses an addition of an oligomeric phosphoric acid ester to a mixture of a polycarbonate and a styrenic resin. Further, U.S. Pat. No. 5,122,556 discloses the use of a polycarbonate and a flame-retardant of a dimeric phosphoric acid ester. Moreover, an addition of such flame-retardant comprising a phosphoric acid ester to a polymer alloy comprising a polycarbonate and a styrenic resin is also disclosed in Japanese Patent Application Laid-open Nos. 62556/1986 (JP-A-61-62556), 4746/1987 (JP-A-62-4746), 115262/1990 (JP-A-2-115262), 298554/1992 (JP-A-4-298554), 179123/1993 (JP-A-5-179123), 262940/1993 (JP-A-5-262940), 279531/1993 (JP-A-5-279531) and so on.
Use of these flame-retardants comprising an aromatic substituted or non-substituted phosphoric acid ester can impart flame-retardancy and impact resistance suitably to a polymer alloy comprising a polycarbonate and a styrenic resin. Therefore, some of such resin composition as a molding material for a home electric apparatus or an OA apparatus has been commercially implemented.
The polymer alloy comprising the non-halogen-containing flame-retardant has, however, frequently poor melt fluidity during the molding process. Accordingly, a shaped article or molded article requiring not only miniaturization but also lightening and thinning can hardly be produced with high efficiency, by imparting high fluidity (flowability) to the polymer alloy.
Further, the polymer alloy is liable to become attached to a mold of the molding machine and thus a frequent cleaning of the mold is required. Deterioration or degradation by residence of the resin by, for example, heat or thermal degradation of the flame-retardant is apt to occur during the molding process.
Furthermore, even if using a polymer alloy having comparatively high melt fluidity, the resultant molded article may have poor light resistance (light stability) and is liable to be discolored. The heat resistance, impact resistance, mechanical strength and the like of the molded article is likely to be decreased when increasing or enhancing the melt fluidity. For instance, the heat resistance and flame-retardancy of the shaped article is liable to be decreased with an increased ratio of the styrenic resin relative to the polycarbonate, although the melt fluidity is enhanced. Accordingly, the light resistance, heat resistance and impact resistance and the mechanical strength of the molded article can hardly be increased with maintaining high melt fluidity.